function changeMenu(obj) {
	var li = obj.parentNode;
	var allItems = document.getElementById("menu").getElementsByTagName("li");
	for(var i=0; i<allItems.length; i++){
		allItems[i].className = "";
	}
	li.className = "selected";
	if(li.id == "first") {
		document.getElementById("left").className = "selected";
	}
	if(li.id == "last") {
		document.getElementById("right").className = "selected";
	}
}